Network Switching Technologies Impairments and Metrics 3 Switching impairments metrics 1 Outline Basic networking technologies Circuit Switching Packet Switching Statistical Multiplexing Virtual Circuit Switching Network impairments The physical environment impacts network protocols Performance Metrics Switching impairments metrics 2 Network Switching Technologies Input Lines 2 Input port 2 Line Card B Switch Fabric Output Lines A A B B C C D Output port 3 Line Card C D Control Line Card Interface Switching impairments metrics 3 Network Switching Technologies Switching transfers information from input ports to output ports Input port 2 Line Card B Elements of Switches Output port 3 Line Card C Line cards multiple interfaces card Switch fabric Control mappings Management Billing Switching impairments metrics 4 Network Switching Technologies Circuit Switching End Office Trunks Local loop Long distance Office Long distance Office End Office On demand call set up Dedicated fixed path Fixed network resources held for call duration Switching impairments metrics 5 Network Switching Technologies Circuit Switching Phases of a call Call establishment Information transfer Call disconnect If no network resources are available the call blocks fast busy signal Network resources can be easily defined e g Voice line Switching impairments metrics 6 Network Switching Technologies Circuit Switching The Public Switched Telephone Network PSTN Dense Wavelength Division DWDM Optical Networks Dial up modems Customers can not use idle channels unused capacity is wasted Switching impairments metrics 7 Network Switching Technologies Message Switching Store Forward Store Forward Store Forward No Dedicated path Address information is added to the message Store if output port is busy Trade off delay for blocking If message is corrupted then retransmit entire message Switching impairments metrics 8 TDM vs Statistical Multiplexing User 1 Dwell time one time slot TDM Link Rate in b s User N Statistical Multiplexing Server User 1 Link Rate in b s User N Server If system empty then immediately TX packet at total link rate Delay wait for turn and then TX packet at total link rate Loss arrive and buffer is full Switching impairments metrics 9 TDM vs Statistical Multiplexing Example Link rate 1 Mb s Message size 5000 bits TDM Frame size 10 ms 1 Mb s 10 ms 10 000 bits 10 times slots frame slot time 1 ms 1000 bits slot Time to transmit 5000 bit message 5 slot times 1 slot frame 50 ms Statistical Multiplexing Assume arriving message finds the system empty Time to transmit 5000 bit message 5000 bits 1Mb s 5 ms Switching impairments metrics 10 Network Switching Technologies Message Switching If message arrives to empty system then it is transmitted at the FULL LINE RATE Transmission at the FULL LINE RATE is shared among the all the users If a message arrives to a busy system it waits Message Server Buffer This is called a Statistical Multiplexer Switching impairments metrics 11 Network Switching Technologies Packet Switching Break up messages into smaller units Packets The process of breaking up larger information units into smaller parts is called Segmentation or Fragmentation The process of putting together smaller parts into larger information units is called Reassembly Segmentation and Reassembly SAR can happen multiple times to the same information stream or flow Switching impairments metrics 12 Network Switching Technologies Packet Switching Output Ports Input Ports Forwarding Table Packet Switch Switching impairments metrics 13 Network Switching Technologies Packet Switching Methods Datagram Packet Switching Conectionless Virtual Circuit Packet Switching Connection oriented Switching impairments metrics 14 Network Switching Technologies Packet Switching Datagrams Each packet is treated independently Packets with same destination may take different routes through the network Each nodes makes independent forwarding decisions No call set up is required Nodes keep no state information No QoS is guaranteed Switching impairments metrics 15 Network Switching Technologies Packet Switching Datagrams User Data inside envelope From Jane Doe Address To John Smith Address Switching impairments metrics 16 Network Switching Technologies Packet Switching Datagrams Store Forward Data Store Forward Store Forward Destination Address Source Address Switching impairments metrics 17 How do Packets find there way Routing and Forwarding routing algorithm local forwarding table header value output link 0100 0101 0111 1001 3 2 2 1 Value in arriving packet s header 1 0111 3 2 Value related to destination Modified from Computer Networking A Top Down Approach Featuring the Internet 4nd edition Jim Kurose Keith Ross Addison Wesley Copyright 1996 2002 J F Kurose and K W Ross All Rights Reserved Switching impairments metrics 18 Network Switching Technologies Packet Switching Datagrams Datagram is an example of a connectionless service Internet Protocol IP provides a connectionless service Switching impairments metrics 19 Network Switching Technologies Virtual Circuit Packet Switching Virtual circuit packet switch is connection oriented Connection oriented does not imply virtual circuits A logical connection is established between the source and destination All packets flow over the same route through the network Packets still statistically share link Switching impairments metrics 20 Virtual circuits signaling protocols used to setup maintain teardown VC used in ATM frame relay X 25 These are Packet Switches application 6 Receive data transport 5 Data flow begins 4 Call connected 3 Accept call network 1 Initiate call 2 incoming call data link physical Modified from Computer Networking A Top Down Approach Featuring the Internet 4nd edition Jim Kurose Keith Ross Addison Wesley Copyright 1996 2002 J F Kurose and K W Ross All Rights Reserved application transport network data link physical Switching impairments metrics 21 Network Switching Technologies Virtual Circuit Packet Switching Forwarding decisions are made based on a virtual circuit identifier not on the full address Packet share transmission facilities Switches save state connection State is saved for duration of the connection QoS can be guaranteed Switching impairments metrics 22 Network Switching Technologies Virtual Circuit Packet Switching Switch 3 Port In 7 VCI In Port Out VCI Out 5 1 55 Note Do not need the same VCI end to end Switching impairments metrics 23 Network Switching